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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Dairy Science

First Advisor

Kenneth Kalscheur


The objective of this study was to investigate the effect of substituting soybean meal products with yeast-derived microbial protein [(YMP) DEMP; Alltech Inc., Nicholasville, KY] in diets containing two forage concentrations. Sixteen Holstein cows (4 primiparous and 12 multiparous) were randomly assigned to a replicated 4 × 4 Latin square in a 2 × 2 factorial arrangement of treatments. Diets contained low (LF; 45% of diet DM) or high forage (HF; 65% of diet DM) and YMP at 0 (NYMP) or 2.25% (WYMP) of the diet. The forage mix consisted of 67% corn silage and 33% alfalfa hay (DM basis). There were no interactions of forage and YMP for any of the production parameters. Cows fed LF consumed more DMI (26.9 vs. 25.2 kg for LF and HF, respectively; P=0.004) and produced more milk (40.1 vs. 37.83 kg; P=0.005) than cows fed HF regardless of the addition of YMP. Milk fat percentage was lower in cows fed LF compared to HF (3.76 vs. 3.94; P=0.04), whereas fat yield tended to be lower (1.52 vs. 1.45 for NYMP and WYMP respectively; P=0.07 in cows fed NYMP . Although milk protein percentage did not differ between forage concentrations with or without the addition of YMP, protein yield and total solids were greater in cows fed LF. Cows fed LF produced more energy-corrected milk (ECM) than those fed HF (41.9 vs. 40.2; P<0.04). Feed efficiency (ECM/DMI) was greater for cows fed NYMP compared to WYMP (1.52 vs. 1.45; P<0.02). An interaction of forage and YMP was observed for propionate concentration, acetate and propionate proportion, and acetate:propionate ratio, as well as a tendency for an interaction of forage and YMP for ruminal pH. A forage effect was observed for ruminal ammonia, isobutyrate concentration, butyrate concentration, isovalerate concentration, as well as proportions of isobutyrate, butyrate, and isovalerate with cows on HF diets having greater concentrations and proportions of these measures. There were no differences in plasma glucose concentrations between forage or YMP levels. There was a forage effect on arterial and venous PUN concentrations. Cows fed the HF diets had greater PUN concentrations. There was a forage effect on the EAA including Ile, Leu, Lys, Met, Thr, and Val. Cows fed the LF diets had greater concentrations of these circulating arterial plasma AA than cows fed the HF diets (P<0.05). A forage effect on circulating concentrations of Ile and Val was observed with cows fed LF diets having greater concentrations of these AA than cows fed HF diets. Cows fed NYMP had greater circulating venous concentrations of Arg, His, Ile, Lys, and Val than cows fed WYMP. These cows also tended to have greater concentrations of circulating venous Thr than cows fed WYMP (P=0.06). The arteriovenous differences of Arg, Ile, Leu, Lys, Met, Phe, and Thr were greater in cows fed LF diets compared to cows fed HF diets. There was also a tendency for the interaction of forage and YMP for the extraction efficiency of Met. Results suggested that the forage level, as well as, YMP affected cow performance. Cows fed NYMP had greater milk fat yield as well as greater feed efficiency. Cows fed LF diets produced more milk and ECM, yet resulted in a lower fat percentage.

Library of Congress Subject Headings

Dairy cattle -- Feeding and feeds
Microbial proteins
Proteins in animal nutrition


Includes bibliographical references (pages 68-78)



Number of Pages



South Dakota State University


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